Thermoconductivity cell



Aug. 28, 1962 R. s. GOHLKE THERMOCONDUCTIVITY CELL 2 Sheets-Sheet 1 Filed 001;. 17, 1960 lllaflv IN V EN TOR.

Qa/ana 5. Goh/Ae iM-gw? #GENT United States Pate 3,950,983 THERMOCGNDUCTIVITY CELL Roland S. Gohlke, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed st. 17, 1960, Ser. No. 63,036 3 Claims. (Cl. 7.3-27) This invention relates to gas-liquid partition chromatography, and more particularly is concerned with a novel, hot-wire thermoconductivity cell for use with chromatography columns which cell permits the collection of gas fractions which have not been in contact with the hot-wire filaments in the gas measuring cavities of the cell.

It is the principal object of the present invention to provide a novel, h.otwire thermoconductivity cell wherein gas fractions can bypass the measuring cavities of the cell.

It is another object of the present invention to provide a novel, hot-wire thermoconductivity cell which not only can be used for normal analytical purposes but which also permits collection of gas samples which have not been in contact with the hot-wire filaments in the measuring cavities of the cell.

It is a further object of the present invention to provide a thermoconductivity cell wherein substantially all or any desired proportion of the gas components flowing through the cell can be diverted from the measuring filament cavities for collection.

These and other objects and advantages of the present invention will become apparent from the detailed description presented hereinafter and by reference to the accompanying drawings.

FIGURE l is a top view of a thermoconductivity cell of the instant invention having the internal passages of the cell designated thereon.

FIGURE 2 is one elevation of the thermoconductivity cell having the internal passageways ofthe cell designated thereon.

FIGURE 3 is a cross-sectional View of the thermoconductivity cell taken along line 3-3 of FIGURE l.

FIGURE 4 shows the by-pass proportioning screw used to control the gas flow in the embodiment of the cell shown in FIGURES 1-3.

FIGURE 5 is chromatogram of a mixture of pentanes wherein all of the gas sample was passed through the measuring cavities of the cell of the instant invention.

FIGURE 6 is a chromatogram of the same mixture of pentanes as shown in FIGURE 5 but wherein the fraction designated by the third recorded peak of the chromatogram was diverted into the by-pass passage for collection without being passed through the filament containing measuring cavities ofthe cell.

The novel and useful therrnoconductivity cell of .the instant invention comprises a body member having internal gas measuring cavities and an internal by-pass gas flow passageway therein. The gas measuring cavities and by-pass liow passage are connected to a common gas delivery tube which tube is fitted with a gas ow control means for controllably diverting the tlow of gas from said gas measuring cavities into said by-pass ow passageways.

One embodiment of the novel thermoconductivity cell of the instant invention is shown in the figures. This 3,050,983 Patented Aug. 28, 1962 particular cell has a body member 11 prepared Vfrom a solid rectangular prismatic block. A threaded female joint 12, was formed, as by drilling and tapping for example, into the center of the top face 13 of the block 11. This joint 12 is threaded to accommodate a coupling (not shown) into which the lower end of a gas chromatography column (not shown) also is attached thereby serving as a means of connecting the chromatography column to the thermoconductivity cell. Extending vertically downward from the center of the bottom Wall 14 of the joint 12 is a tubular passageway, or gas deliveryA tube, 15. This passageway passes throughout the length of the block 11. Near the top of the passageway 15, below the joint 12, small diametered passages 16:1--16b extend substantially laterally outward from opposite sides of the passageway 15. The passages 16a-16h lead to the gas measuring cavities 17a-17b and open into these cavities near their ends 18a-18b. The cavities 17a-17b exit respectively from opposite sides 19 and Ztl of the block 11. These measuring cavities are tapered downward from the horizontal at an angle of about 15 thereby permitting drainage of any liquids that might condense in these cavities during operation. The shoulders 21a-2lb respectively of the cavities 17a-17h are threaded to precisely accommodate the jacketed glass insulator of a standard hot-wire filament assembly such as the type 9225 sold `by `the Gow-Mac Instrument Company (not shown). Discharge tubes 22a-22b lead respectively from the filament cavities 17a-17h into a common discharge passage 23 for removal of the spent gases from the measuring cavities. This passage 23 extends vertically downward below the passage 22h and exits from the bottom 24 of the block 11.

Below the point at which the small passages 16a-leb extend laterally outward from the entrance tube 15, this passageway 15 is enlarged in diameter through `a tapered `shoulder 25. The enlarged portion 26 of the passage 15 below the shoulder 25 extends downward through a portion of the block 11. This portion 26 of the p-assage 15 in turn throughout the distance covered by approximately the bottom third of the block is machined and tapped to produce a thread assembly 27. This assembly 27 mates with the threads 2S of a by-pass proportioning screw 29.

A by-pass tubular gas collection passageway 30 leads outwardly and downwardly from passage 15 starting from near the top of the enlarged portion 26 of the passage 15 but below the small diametered passages 16a-16b and exits from the bottom 24 of the block 11. This passage is independent of the discharge passage 23.

Additionally, the cell is fitted with a separate conventional reference gas ilow system 31.

The by-pass proportioning screw 29 has a threaded center portion 28 which mates with threads 27 in the bottom of passage 15 of block 11. The forward part 32 of the screw 29 is reduced in cross-section to be accommodated by the portion 26 of the passage 15 and this forward portion 32 has a tapered tip 33 which mates with the tapered shoulder 25 of the shaft 15. The tapered tip 33 and tapered shoulder 25 are so designed that when in mating position they form an eiective needle valve and valve seat assembly respectively thereby providing a gas ow control means.

The cell body 11 can be of any one of a wide variety of useful structural materials including for example brass, stainless steel, aluminum, magnesium, quartz, glass, nickel, titanium, ferrous alloys, low carbon steels, cobalt containing alloys and the like.

It is apparent from the complexity of the internal passage systems in the novel thermoconductivity cell of the instant invention that a number of these passages are most easily prepared by drilling or otherwise machining `from the outside of the block in towards the center. This operation leaves undesired passage extensions opening onto the outer faces of the block. These openings and extensions conveniently can be sealed oif by conventional techniques and materials such as silver soldering, brazing, thermally resistant cements, etc. thereby giving the desired passage system within the cell.

Furthermore, it is understood that the cell of the instant invention can be prepared by other means such as casting, utilizing recognized methods of integrally casting passageways therein for the casting operation.

In using the novel thermoconductivity cell of the instant invention, for normal analytical operations the by-pass proportioning screw 29 is adjusted so that its tip 33 mates -tightly with the tapered shoulder 25 of the shaft 15 thereby closing otI the by-pass passage Sil. When the screw 29 is in this position, all of the gas from the chromatographic column passes through the measuring filament cavities. On the other hand, if it is desired to collect a designated portion or substantially all of the gases coming from the chromatographic column, the screw 29 of the gas by-pass control means is turned so that an opening exists between the tip 33 and the tapered shoulder 25 of the shaft 15. Because of the relative size diiferential in the diameter of the larger by-pass passage 30 and the smaller diametered gas feed passages lea- 16b leading from the upper section of the gas delivery tube 15 to the lament cavities 17a-l7b, gas flow into the by-pass 30 is favored even rwhen the needle valve is opened only a small amount. Therefore, in order to direct gases into the measuring cavities 17a-171: the needle valve must be closed entirely or closed to such 'an extent that a back pressure is exerted on the gases emanating from the chromatography column. In actual operation, it is advisable to maintain a slight gas flow through the measuring cavities at all times as failure to do this can result in diffusion of sample components into the measuring iilament cavities. Additionally, total stoppage of the gas ilow through the iilament cavities and over the filaments could result in filament failure when operating the system at high bridge currents. These latter problems are avoided if only a very small amount of the gas from the chromatographic column is passed through the filament cavities, this amount being as low as one cubic centimeter per minute at STP.

The actual collection of the gas fraction through the by-pass passageway is improved further if the small amount of gas owing through the measuring cavities acts against a slight pressure head. The establishment of this pressure head easily may be accomplished, for example, by dipping the measured gas exit tube (not shown, or an extension of it) about 1/16 of an inch below the Surface of Water, and then adjusting the by-pass screw 29 until the desired amount of gas is being passed through this measured gas exit tube. It is convenient to attach a soapbubble flow meter to the by-pass tube tot facilitate making this adjustment.

The utility of the gas by-pass assembly of the instant cell is shown by the comparative chromatograms presented in FIGURES and 6. FIGURE 5 relates to a chromatogram of a mixture of pentanes wherein all of the gases flowing from the chromatographic tube were passed through the measuring lament cavities, over the laments Vand then discharged from the conductivity cell. FIGURE 6 shows a chromatogram of the same mixture of pentanes wherein gas components represented by the third recorded peak of the chromatogram of FIGURE 5 were `sent through the b y-pass for collection. To accomplish this gas collection, the gas sample was loaded intothe column and the analysis started, the needle valve being closed. The proportioning screw was opened at the point indicated on the FIGURE 6` to permit diversion of substantially all of the sample stream through the by-pass collection passage. (A small portion of the peak was allowed to pass through the measuring cavities both to prevent component diffusion and filament breakdown as discussed hereinbefore as well as to serve as a guide to establish when this fraction of gas had passed.) After passage of the desired fraction, as shown by the chromatogram, the -by-pass screw again was closed and the -two remaining peaks were analyzed without collection. The amount of gas taken off through the by-pass for collection had no effect upon the development of the chromatogram. This fact can be observed by a careful comparison of the conventional chromatogram of FIGURE 5 and that for the by-passed sample, FIGURE 6, wherein it can be seen that the residence times of all the peaks are in precise coincidence.

Various modiiications can be made in the apparatus of the present invention without departing from the spirit or scope thereof for it is understood that I limit myself only as defined in the appended claims.

I claim:

l. A thermoconductivity cell which comprises a body member having internal gas measuring cavities and an internal by-pass gas flow passageway therein, said gas measuring cavities and said by-pass gas flow passageway being connected independently to a common gas delivery tube, the junction of said lby-pass gas llow passageway and said gas delivery tube being downstream from said gas measuring cavities, said gas delivery tube being fitted with a gas How control means above said junction of said by-pass gas ow passageway and said gas delivery tube, said gas flow control means controllably diverting the flow of gas from said gas measuring cavities into said bypass ow passageway.

2. A thermoconductivity cell for a chromatographic assembly which comprises `a body member, said body member having therein a means for connecting a chromatographic column thereto, a gas delivery tube extending vertically downward from said connecting means throughout the length of said body member, two passages extending outwardly from opposite sides of said gas delivery tube near the top of said tube, two gas measuring cavities connected to said gas delivery tube near said connecting means through the outwardly extending passage, a gas by-pass passageway connected to said gas delivery tube below the outwardly extending passages, said gas by-pass passageway extending downward through said body member, ya gas flow control means, said control means fitted in said gas delivery tube above the junction of said gas delivery tube and said gas by-pass passageway, said control means controllably diverting the iiow of gas from said gas measuring cavities into said gas bypass passageway.

3. A thermoconducctivity cell for use with gas chromatognaphy column which comprises a rectangular, prismatic block-like body member, said body member having a threaded, female joint in the center of the top face, a gas delivery tube extending vertically downward from the center of the bottom wall of said joint and passing throughout the length of the block, said ftube being enllarged in diameter through a tapered shoulder below said joint Iand having a threaded portion at its lower end, two small-diametered passages extending substantially laterally outward from opposite sides of said gas delivery tube below the bottom wall of said joint `and above said tapered shoulder of said tube, two gas measuring cavities connected to said gas delivery tube one each through one of the small-diametered passages leading from said delivery tube, -a discharge tube leading from each of` said gas measuring cavities to a common spent gas discharge passage, said discharge passage extending downward through said block, a by-pass tubular gas collection passageway leading outwardly from near the top of saidl gas delivery tube below said srnall-diarnetered passages, said bypass tubular passageway extending downwardly through said body member independently of said spent gas discharge passage, a by-pass proportioning screw, said screw having a threaded portion Jthe threads of which mate with the threaded Iportieri of said gas delivery tube and a forward part ending in a tapered tip, said tip mating with the tapered shoulder of said delivery tube and 10 2,404,993

6 forming a needle valve and valve seat assembly therewith whereby gas ow controllably is diverted from said measuring cavities to said by-pass gas collection passageway, and, a separate conventional reference gas ow system.

References Cited in the le of this patent UNITED STATES PATENTS Oetjen Apr. 10, 1934 Krogh Feb. 15, 1944 Sullivan July 30, 1946` 

